I. Field of the Invention
The present invention relates to telecommunications, and more particularly to wireless communications.
II. Description of the Related Art
Wireless communications systems employ a number of geographically distributed, cellular communication sites or base stations. Each base station supports the transmission and reception of communication signals to and from stationary or fixed, wireless communication devices or units. Each base station handles communications over a particular region commonly referred to as a cell/sector. The overall coverage area for a wireless communications system is defined by the union of cells for the deployed base stations. Here, the coverage areas for adjacent or nearby cell sites may overlap one another to ensure, where possible, contiguous communications coverage within the outer boundaries of the system.
When active, a wireless unit receives signals from at least one base station over a forward link or downlink and transmits signals to at least one base station over a reverse link or uplink. There are many different schemes for defining links or channels for a cellular communication system, including, for example, TDMA (time-division multiple access), FDMA (frequency-division multiple access), and CDMA (code-division multiple access) schemes. In CDMA communications, different wireless channels are distinguished by different channelization codes or sequences that are used to encode different information streams, which may then be modulated at one or more different carrier frequencies for simultaneous transmission. A receiver may recover a particular stream from a received signal using the appropriate code or sequence to decode the received signal.
For voice applications, conventional cellular communication systems employ dedicated links between a wireless unit and a base station. Voice communications are delay-intolerant by nature. Consequently, wireless units in wireless cellular communication systems transmit and receive signals over one or more dedicated links. Here, each active wireless unit generally requires the assignment of a dedicated link on the downlink, as well as a dedicated link on the uplink.
With the explosion of the Internet and the increasing demand for data, resource management has become a growing issue in cellular communication systems. Next generation wireless communication systems are expected to provide high rate packet data services in support of Internet access and multimedia communication. Unlike voice, however, data communications may be relatively delay tolerant and potentially bursty in nature. Data communications, as such, may not require dedicated links on the downlink or the uplink, but rather enable one or more channels to be shared by a number of wireless units. By this arrangement, each of the wireless units on the uplink competes for available resources. Resources to be managed in the uplink include the received power at the base station, and the interference created by each user to other users in the same sector or cell, as well as in other sectors or cells, for example. This is in contrast to the resources to be managed on the downlink, including fixed transmit power budgets.
While data communications may be relatively delay tolerant and potentially bursty in nature, one problem expected in the next generation wireless communication systems is failed data block or data packet transmission. More particularly, a base station, for example, may unsuccessfully transmit one or more data packets from a number of packets to an identified wireless unit. As a result of this failure, the base station may use any number of retransmission techniques, such as hybrid automatic repeat request (“HARQ”), for example, to deliver the data packet(s) not satisfactorily received by the wireless unit. While the base station attempts retransmission of previously unsuccessful transmitted packets, other data packets may be, however, subsequently transmitted to the wireless unit.
In High Speed Downlink Packet Access (“HSDPA”) systems, each wireless unit employs a timer set by the base station. Packet data is sent from the base station to the wireless unit in a sequential manner. Upon satisfactory reception, the wireless unit delivers the packet data from its buffer for processing in the same sequential order. If, during reception, the wireless unit determines that a gap in the sequence order of the received data packets has occurred, the wireless unit then starts a timer for the missing data packet(s). The timer provides a time window in which the wireless unit waits for the satisfactory reception of each data packet, perceived as missing, by transmission and/or a retransmission scheme(s). If the retransmission scheme fails to satisfactorily deliver the missing data packet(s) to the wireless unit before the timer window passes, the wireless unit assumes the packet(s) to be lost.
Data packets may be lost for various reasons. In one scenario, the base station may determine that the maximum retransmission attempts for a data packet have been exceeded and no further retransmission are permissible. Secondly, the base station may decide to unilaterally abort the transmission or retransmission of the data packet(s). Thirdly, the base station may determine that its resources are needed for a higher priority customer(s) or higher priority data, and therefore may terminate the transmission and/or retransmission of the “missing” data packet. Fourthly, the wireless unit may receive the transmitted data packet with an error. Here, the wireless unit transmits a NACK (e.g., a negative acknowledgment to indicate reception of a data packet with errors), though the base station mistakenly receives an ACK (e.g., a positive acknowledgment indicating the wireless unit received the data packet satisfactorily) instead and, thusly, no retransmission will occur in the base station.
Consequently, in HSDPA systems, the base station may determine the missing one or more data packets as lost at any point of the transmission and/or retransmission. In contrast, however, the wireless unit will not ascertain the missing data packet(s) as lost until after the timer expires. Consequently, the wireless unit has to wait until the timer expires before processing the received data packets, and/or attempting to recover the lost packet(s) by various other techniques. This delay or waiting time for the timer to expire is sometimes referred to as a stall period.
The length of the stall period may be relatively substantial in time. The base station may determine the missing packet as lost by, for example, aborting its retransmission or determining to serve higher priority customer(s) or higher priority data, in significantly less time than the setting of the timer by the base station. It should be noted that the timer is initially set conservatively such that the wireless unit may handle a predetermined number of retransmission attempts for missing data packets. Due to the randomness of the completion time of each transmission, the time to complete a designated number of retransmission attempts may vary. Consequently, the timer is set conservatively so that valid transmissions may not be terminated prematurely.
As a result of the hereinabove, a demand exists for a method supportive of efficient, high-speed data communications that avoids or minimizes unnecessary delays. Moreover, a need exists for a method of minimizing the effects of a stalling condition period in wireless units.